Several studies have found that an inordinate amount of potential instructional time is lost in the American secondary school classroom. This paper briefly overviews the history and types of block scheduling in secondary schools and presents findings of a study that examined the perceptions of administrators and teachers in two large eastern Tennessee high schools that implemented block scheduling. The schools changed from a traditional six-period school day to a four-block school day, in which students took four 90-minute classes daily for 90 days. Data were gathered by a survey of 238 teachers and 10 administrators, which yielded response rates of 86 and 60 percent, respectively. Interviews were also conducted with six teachers and four administrators. Most of the teachers and all of the administrators agreed that the staff was adequately prepared for the transition; the staff required more preparation time; and the staff used a wider variety of instructional delivery approaches. Administrators and teachers did not want to abandon the four-by-four block schedule and return to the traditional schedule. Two tables and a copy of the questionnaire are included. (Contains 13 references.) (LMI)